The present invention relates to a cereal-grain polishing apparatus of vertical type in which cereal grains are polished during upward movement thereof through a polishing chamber defined between a perforated tubular member and a so-called friction-type polishing roll.
A cereal-grain polishing apparatus of the kind referred to above is known from, for example, Japanese Patent Application Laid-Open No. 63-7849 filed in the name of the assignee of this application. In the known apparatus, a perforated tubular member is arranged substantially vertically. A polishing roll fixedly mounted to a rotary shaft is rotatably arranged within the perforated tubular member to define a polishing chamber between a peripheral wall of the polishing roll and the perforated tubular member. The peripheral wall of the polishing roll cooperates with a peripheral surface of the rotary shaft to define therebetween a hollow space. The polishing roll is provided with at least one vertically extending, elongated agitating projection and at least one vertically extending, elongated opening communicating with the hollow space. Cereal grains to be polished are forcibly supplied to a supply position below a lower end of the polishing chamber. A screw feed roll is fixedly mounted to the rotary shaft at a location below the polishing roll, for feeding cereal grains to the polishing chamber from the supply position. Thus, the cereal grains are caused to move upwardly through the polishing chamber.
In operation, when the polishing roll is rotated, the agitating projection on the polishing roll brings the cereal grains within the polishing chamber, into friction contact with each other to remove surface layers from the respective cereal grains, thereby polishing the same. Air is caused to flow from the hollow space between the rotary shaft and the polishing roll, to a surrounding space around the perforated tubular member through the elongated opening in the polishing roll, the polishing chamber and the perforations in the perforated tubular member, to carry the removed surface layers of cereal grains out of the polishing chamber to the surrounding space.
The cereal-grain polishing apparatus described above is excellent in that because the cereal grains are forcibly supplied to the supply position, an amount of cereal grains fed to the polishing chamber is stabilized, making it possible to avoid lack of uniformity in polishing of the cereal grains due to insufficient supply thereof to the polishing chamber.
However, the conventional cereal-grain polishing apparatus yet leaves room for further improvement. That is, there is a possibility that during polishing of the cereal grains within the polishing chamber, some cereal grains enter the hollow space within the polishing roll from the polishing chamber through the elongated opening, and are accumulated on the bottom of the hollow space. The accumulated cereal grains sometimes cause eccentric rotation of the polishing roll, resulting in non-uniform polishing of the cereal grains. Moreover, during polishing of cereal grains of a different variety, the previously accumulated cereal grains are returned to the polishing chamber through the elongated opening and are mixed with the cereal grains of the different variety. For instance, nonglutinous rice is mixed with glutinous rice.